A moldable composite sheet having improved thermal and mechanical property characteristics. In one aspect, the composite sheet may be a porous fiber-reinforced thermoplastic resin comprising discontinuous mineral reinforcing fibers, and one or more skin layer materials. Generally, the composite sheet may have a void content or porosity from about 5% to about 95% by volume of the sheet, an areal weight between about 400 g/m2 to about 4000 g/m2 (gsm), a mineral fiber content from about 20% to about 80% by weight, and a thermoplastic resin content from about 20% to about 80% by weight of the composite sheet. The composite sheet can be molded via low pressure processes, such as thermoforming, match metal molding on stops, vacuum forming and pressure forming, to produce durable automotive interior trim parts and construction articles having improved thermal and mechanical properties in addition to other beneficial characteristics.